Typically, a blind transport system will have a top head rail which both supports the blind and hides the mechanisms used to raise and lower or open and close the blind. Such a blind system is described in U.S. Pat. No. 6,536,503, Modular Transport System for Coverings for Architectural Openings, which is hereby incorporated by reference. In the typical top/down product, the raising and lowering of the blind is done by a lift cord suspended from the head rail and attached to the bottom rail (also referred to as the moving rail or bottom slat). The opening and closing of the blind is typically accomplished with ladder tapes (and/or tilt cables) which run along the front and back of the stack of slats. The lift cords (in contrast to the tilt cables) usually run along the front and back of the stack of slats or through holes in the middle of the slats. In these types of blinds, the force required to raise the blind is at a minimum when the blind is fully lowered, since the weight of the slats is supported by the ladder tape so that only the bottom rail is being raised at the onset. As the blind is raised further, the slats stack up onto the bottom rail, transferring the weight of the slats from the ladder tape to the lift cords, so progressively greater lifting force is required to raise the blind as the blind approaches the fully raised position.
Some window covering products are built in the reverse (bottom/up), where the moving rail, instead of being at the bottom of the window covering bundle, is at the top of the window covering bundle, between the bundle and the head rail, such that the bundle is normally accumulated at the bottom of the window when the opening is uncovered and the moving rail is at the top of the window covering, next to the head rail, when the window opening covered. There are also composite products which are able to do both, to go top/down and/or bottom/up.
In contrast to a blind, in a typical top/down shade, such as a shear horizontal window shade, the entire light blocking element wraps around a rotator rail as the shade is raised. Therefore, the weight of the shade is transferred to the rotator rail as the shade is raised, and the force required to raise the shade is thus progressively lower as the shade (the light blocking element) approaches the fully raised (fully open) position. Of course, there are also bottom/up shades and also composite shades which are able to do both, to go top/down and/or bottom/up. In the case of a bottom/up shade, the weight of the shade is transferred to the rotator rail as the shade is lowered, mimicking the weight operating pattern of a top/down blind.
Most shades may have a single covering or light blocking element which is either extended or retracted, such as a roller shade. However, there is also a type of shade which may be referred to as a variable light control shade, wherein the light-controlling element is composed of several sub-elements resembling the slats in a blind. In this type of shade, in addition to extending and retracting the overall light-blocking element, these slats may be moved relative to each other, tilting them open or closed to effect variable light control.
A wide variety of drive mechanisms is known for raising and lowering blinds and shades, and for tilting their slats. A cord drive to raise or lower the blind is very handy. It does not require a source of electrical power, and the cord may be placed where it is readily accessible, getting around many obstacles.
At this point, it is beneficial to explain that the cord (or cords) in a cord drive may be the same lift cord which attaches to the bottom slat (or bottom rail) of the blind, or the drive cords and lift cords may be totally separate and independent. To avoid confusion, we will henceforth refer to the cords attached to the cord drive as drive cords, while the cords attached to the bottom rail will be referred to as lift cords, with the understanding that, in some embodiments, the drive cord and the lift cord may be the same cord.
Known cord drives have some drawbacks. The cords in a cord drive, for instance, may be such that they are either hard to reach when the cord is way up (and the blind is in the fully lowered position), or the cord may drag on the floor when the blind is in the fully raised position.